Cancer-associated cachexia is a condition defined by a sustained net-negative energy imbalance. Although the different types of adipose tissue – white, beige, and brown – have been implicated in contributing to cancer-associated cachexia, the mechanisms of these maladaptive changes and their impact on whole-body energy expenditure have not been fully elucidated. Using breast cancer as our model, we demonstrate white adipose tissue browning in murine and human breast cancer; furthermore, we demonstrate that this effect is extremely localized and takes place early in tumor progression. We utilized in vitro cell culture techniques and demonstrate that cancer secreted factors and cross-talk with white adipocytes decrease expression of classic white adipose tissue-related genes. We also demonstrate in murine and human culture models that cancer secreted factors reduce white adipocyte lipid droplet size, and cross-talk between cancer cells and adipocytes results in an increase in lipolysis-related gene expression. Interestingly, our results strongly suggest that in mice, neither cancer secreted factors nor cross talk with adipocytes can induce white adipose tissue browning, indicate that this process likely occurs independently of direct cancer interactions with local white adipocytes. We demonstrate that interleukin 6, a cytokine with previous implications in white adipose tissue browning, induces interleukin 6-mediated signaling; however, that signaling alone is not enough to directly induce white adipose tissue browning. We present preliminary data suggesting that immune cell population shifts within the white adipose tissue of mice with breast cancer tumors may be source of white adipose tissue browning. We show that the Virginia Commonwealth University Health System has an identifiable population of patients with cancer with what we hypothesize as maladaptive thermogenic adipose tissue activity, and discuss ongoing experiments aimed at understanding the implications of these changes on whole body energy expenditure in human patients. Lastly, in a case of autoimmune diabetes mellitus in the setting of an extra-adrenal paraganglioma, we demonstrate that the interaction between cancer and whole-body metabolism is multifaceted. Together, these experiments demonstrate that adipose tissue plasticity occurs in breast cancer (and other cancers), and that different drivers for individual changes exist within the tumor microenvironment. We predict that further exploration of the exact mechanisms and translational implications will provide useful information to lead to new therapeutic treatments for patients with cancer-associated cachexia.

Abstract Obesity is associated with greater risk of several diseases, such as type 2 diabetes and metabolic syndrome. Single nucleotide polymorphisms (SNP) within the fat mass- and obesity-associated gene FTO are robustly associated with increased body mass index (BMI) in several age and ethnic groups. Studies with transgenic mice support a mechanistic role for FTO protein in energy metabolism. Fto-deficient mice are leaner than wild-type and overexpression of Fto leads to obese phenotype; however, the precise mechanism of FTO action in the control of BMI has remained obscure. Fto mRNA is most abundant in the brain while high expression is present also in white and brown adipose tissues (WAT and BAT, respectively). WAT stores the nutritional energy and BAT dissipates it to produce heat. Furthermore, these organs participate in a complex endocrine network affecting the whole body metabolism, which is more or less disrupted in obesity. In the browning process, white adipocytes begin to manifest brown characteristics. MicroRNAs (miRNA) are small RNA molecules, which fine-tune post-transcriptionally the expression of genes important in several cellular processes, including WAT and BAT differentiation and browning of WAT. FTO has been shown to participate in these processes as well as miRNA regulation. The current study used a new Fto-deficient mouse model to reveal deeper insights into the role of Fto on genes affecting WAT and BAT differentiation and function, as well as WAT browning. Furthermore, the effects of Fto on the miRNA regulation in WAT browning and BAT were investigated. Our results supported a role for Fto in adipose tissue. Fto-deficient mice were resistant to diet-induced obesity and their WAT and BAT adipocytes did not become hypertrophic similar to wild-type on high-fat diet. Furthermore, the expression of genes affecting adipose tissue differentiation and function was altered in Fto-deficient WAT and BAT, especially after high-fat diet, and the changes may be mediated via altered miRNA expression. Fto-deficient WAT was more susceptible to browning, which in part contributed to the lean phenotype of these mice. Current study supported a role for Fto in whole body metabolism and adaptation of adipose tissue to changes in dietary environment. / Tiivistelmä Lihavuus on toistuvasti yhdistetty useisiin liitännäissairauksiin, kuten tyypin 2 diabetekseen ja metaboliseen oireyhtymään. FTO-geenissä (fat mass- and obesity-associated) esiintyvien yhden nukleotidin muutoksien (single nucleotide polymorphia, SNP) on useissa ikä- ja etnisissä ryhmissä raportoitu liittyvän korkeampaan painoindeksiin ihmisillä. Muuntogeenisillä hiirillä tehdyt tutkimukset tukevat FTO:n mekanistista roolia energia-aineenvaihdunnassa, sillä Fto-poistogeeniset hiiret ovat villityypin hiiriä laihempia ja sen yliekspressio johtaa ylipainoon. FTO:n tarkka rooli painon säätelyssä on kuitenkin vielä epäselvä. Fto:ta tuotetaan eniten aivoissa, mutta myös valkoisessa ja ruskeassa rasvassa. Valkoinen rasva varastoi ravinnosta saatavan energian ja ruskea hajottaa sitä lämmöntuotantoon. Näillä kudoksilla on lisäksi tärkeä rooli energia-aineenvaihdunnan monimutkaisessa verkostossa. Valkoisen rasvakudoksen ruskettumisprosessissa valkoiset rasvasolut alkavat muistuttaa ruskeita rasvasoluja. Mikro-RNA:t (miRNA) ovat pieniä RNA-juosteita, jotka hienosäätävät geenien ekspressiota transkription jälkeen ja vaikuttavat useisiin solun tärkeisiin tapahtumiin, myös valkoisen ja ruskean rasvasolun erilaistumiseen ja ruskettumiseen. FTO osallistuu näihin prosesseihin sekä miRNA-säätelyyn. Tämän tutkimuksen tavoitteena oli selventää Fto:n roolia valkoisen ja ruskean rasvakudoksen erilaistumisessa ja toiminnassa Fto-poistogeenisen hiirimallin avulla. Lisäksi selvitettiin Fto:n vaikutuksia valkoisen rasvan ruskettumiseen ja ruskean rasvan toimintaan osallistuvien miRNA:iden säätelyyn. Tulokset tukivat FTO:n roolia rasvakudoksessa. Fto-poistogeeniset hiiret eivät lihoneet rasvaisella ruokavaliolla eivätkä niiden rasvasolut varastoineet rasvaa yhtä paljon kuin villityypin hiirillä rasvaisen ruokavalion jälkeen. Lisäksi Fto-poistogeenisen rasvakudoksen erilaistumiseen ja toimintaan liittyvien geenien esiintyvyys muuttui erityisesti rasvaisella ruokavaliolla. Nämä muutokset voivat osittain selittyä muuttuneella miRNA-säätelyllä. Tulokset viittasivat siihen, että Fto-poistogeeninen valkoinen rasvakudos oli alttiimpaa ruskettumiselle, mikä osaltaan vaikutti Fto-poistogeenisten hiirten laihuuteen. Tutkimus tuki Fto-geenin roolia energia-aineenvaihdunnan säätelyssä sekä rasvakudoksen mukautumisessa ruokavalion muutoksiin.